Method and apparatus for heat treating metal stock



'July 15, 1958 J. H. KUNz, JR 2,843,514

iiil lllllllllllllllllllllllll :i AI n l Hann/1111111111 INVENTOR John Henry Kunz, Jr.

BY mfmmdmmfmmw @AZ ATTO YS RNE United States Patent O METHOD AND APPARATUS FOR HEAT TREATING METAL STOCK John Henry Kunz, Jr., Waterbury, Conn., assignor to The American Brass Company, Waterbury, Conn., a corporation of Connecticut The invention relates to furnaces and more particularly to annealing furnaces of the bell or retort type. The invention aims to provide an improved method of, and instrumentalities for, the cooling of annealed or heattreated metal stock within the bell or retort".

The bell furnace may be either circular or rectangular and is customarily provided with a motor-driven fan for heating and cooling by forced convection currents. Such furnaces are used for the annealing or heat-treatment of coiled metal strip (e. g., steel, copper, brass, etc.), wire in coils or on spools, sheet and bar stock, miscellaneous parts loaded in baskets, and the like. The metal stock to be heat-treated is loaded on a platform or the like and covered by the bell or retort. The furnace or heating element is then lowered over the bell and the heating cycle begins. At the completion of the heating cycle, the heating element is removed and the heat-treated metal stock is permitted to cool within the bell in a controlled circulating atmosphere. Three or more bases or bell stations are ordinarily required for each 4heating element to provide for loading (and unloading), heating and cooling.

In the heretofore customary practice of annealing copper and brass in a bell furnace, the heating cycle has been about 5 hours and the cooling cycle about 17 hours. Since the cooling cycle is more than three times as long as the heating cycle, 5 bases or bell stations are provided for a single furnace. Due to the extended cooling time, little incentive has existed to decrease the annealing time.

The present invention effects a very substantial reduction in the time required for cooling heat-treated metal stock in a bell furnace. In accordance with the invention, a spray of water is directed against the rotating fan blades within the bell, after the heating cycle has been completed and the heating element has been removed. Due to the high temperature within the bell, the water of the spray is immediately vaporized. Simultaneously, an inert gas is introduced and circulates within the bell, and inert gas and water vapor (resulting from vaporization of the water spray) are exhausted from within the bell. When the temperature of the metal stock undergoing cooling has fallen until its residual heat is only slightly greater than required to vaporize water, say to a temperature within the range of about 110 C. and about 125 C., the water spray is discontinued while continuing the introduction and exhaustion of the inert gas until water vapor has been substantially completely exhausted from within the bell, and the temperature of the metal stock is suiciently low to permit exposure to the atmosphere. The bell is then removed and the cooled metal stock is exposed to the atmosphere for unloading from the furnace. By practice of the invention, copper and brass stocks annealed at a temperature of 400 to 500 C. in a heating cycle of about 5 hours have been cooled to atmospheric temperatures in from 4 to 5 hours with metal stock loads varying from 13,000 to 22,000 pounds. The combined heating and cooling cycle is thus reduced from 22 to 9-10 hours, a time saving of 12-13 hours.

The invention will be better understood from the "lee 2 following description taken in conjunction with the accompanying drawing in which the single figure is a digrammatic elevation, partly in section, of a bell furnace with the heating element removed.

As illustrated in the drawing, the bell furnace is ready for cooling the heat-treated metal stock 5, which may be a coil of wire or the like. The heating element has been removed and, hence, is not shown in the drawing. As well understood by those skilled in the art, the heating element, lowered by a crane or the like, encloses and covers the bell 6 during the heating cycle, and upon completion of the heating cycle is raised from the bell and moved to another bell station. The heating element is provided with any suitable type of heating means, such as gas or oil fuel, electric heating elements, etc. The bell 6 is thus externally heated, as in a retort or muliie furnace, and heat is conveyed from the hot wall of the bell to the metal stock by convection currents Within the bell. A controlled inert atmosphere is usually maintained within the bell during the heating cycle and circulation of this atmosphere by the fan assures rapidlymoving convection currents.

With both the heating element and the bell raised, the metal stock 5 to be heat-treated is loaded upon a platform or bottom plate 7. The bell 6 is then lowered, e. g., by a crane, and its lower edge or apron 6 dips well beneath the surface of a body of water 8 in a sealing pit or moat 9 surrounding the base 10 supporting the platform 7. The platform is spaced from the base suiiiciently to accommodate the blades 11 of a fau driven by a motor 12 suitably mounted in the base. The heating element is then lowered over the bell, the heating cycle is carried to completion, the heating element is removed, and the hot heat-treated metal stock is cooled by the improved method of the invention.

In accordance with the invention, a nozzle 13 is positioned beneath the platform 7 to direct a spray of water against the rotating fan blades 11. The nozzle is adapted to beconnected by a pipe 14 and flexible hose 14 to a suitable source of water under pressure. The pipe 14 is provided with a conveniently located valve 15 and pressure gauge 16.

A gas inlet pipe 17 extends through the base 10 into the space between the base and the platform 7 and is provided with a control valve 18. The gas pipe 17 is surrounded by an exhaust gas pipe 19, also terminating in the space between the base 10 and platform 7 and provided with a control valve 20. A thermo-couple 21, or other suitable temperature-responsive means, is thermally associated with the metal stock 5 and is operatively connected by a cable 22 to a temperature-indicating instrument 23 conveniently located outside the furnace. A second thermo-couple 24, or other suitable temperature-responsive device, is positioned within the bell 6 remote from the stock 5 in a location fairly indicative of the average air or atmosphere temperature within the bell. The thermo-couple 24 is connected by a cable 25 to a temperature-indicating instrument 26 also conveniently positioned outside the furnace.

It has heretofore been customary to artifrcally cool the bell 6 by water supplied near the top of the bell from an overhead pipe 27, which may be permanently positioned at the bell station or may be portable and placed in operative position with respect to the bell when the heating element has been removed. Even with cooling water so supplied, the dissipation of heat from within the bell is so slow that metal stock heat-treated to a temperature around 400 C. cannot be cooled to a sufficiently safe temperature for exposure to the atmosphere in less than about 17 hours.

In accordance with the present invention, the nozzle 13 directs a spray of water against the rotating fan blades 11. This causes an extremely rapid drop in the temperature within the bell. In conjunction with the heretofore customary overhead sprinkler system 27, the invention permits lowering of the air or atmosphere temperature within the bell (as indicated by instrument 26) at least 200 C. in approximately 1/2 hour.

Vaporization of the water sprayed against the rotating fan blades 11 extracts heat from within the bell `and circulation of the resulting water vapor or steam rapidly cools the mass of metal stock undergoing coolingon the platform 7. The platform 7 is itself a large massof metal and is normally the hottest part within the bell. Since the water spray is directed at the rotating fan blades 11 under the platform 7, this large mass of ymetal is quickly cooled.

During the spraying of water against the rotating fan blades 11, an inert gas, such as illuminating gas, nitrogen, or the like, is introduced Within the bell 6 through the pipe 17, and the inert gas along with water vapor formed by vaporization of the water spray are exhausted `from the bell through the pipe 19, whereby during the cooling cycle a controlled inert atmosphere is maintained Within the bell. When the temperature of the metal stock 5 has fallen until its residual heat is only slightly greater than required to vaporize water, say a temperature of about 110 C. to about 125 C., as indicated by the instrument 23, the water spray is discontinued by closing the Valve 15, without interrupting the supply and exhaustion of the inert gas. The continued circulation of the inert gas Within the bell exhausts all of the remaining water vapor and eliminates any possibility of water-staining the heat-treated stock. When the temperature of the metal stock 5 has fallen to about atmospheric temperature, as indicated by the instrument 23, or in the case of some metal stocks to a somewhat higher temperature, e. g. 50 to 85 C., the valves 18 and 20 are closed, water is drained from the pit 9 through a valved drain pipe 23, the bell 6 is raised or pulled, and the cooled metal stock is unloaded from the platform 7.

When the heating cycle has been completed, the gas supply valve 18 and gas exhaust valve 20 are turned on full, the heating element is removed, and the inside water spray valve 15 is slowly and gradually opened until the water pressure is raised to about 70 pounds per square inch (p. s. i.). Simultaneously, the overhead sprinkler 27 is slowly and gradually turned on. When the temperature of the metal stock has fallen to around 110 to 125 C., the overhead sprinkler is turned off and the valve 15 is closed. When the metal stock temperature has fallen to around 80-90 C., with the gas supply and exhaust valves 18 and 20 still open, the valve in the drain pipe 28 is opened and Water is drained from thepit until the Water seal is broken, the valves 18 and 20 in the meantime being closed. The bell may then be raised.

The following examples illustrate practices of the invention on copper alloys following an annealing heating cycle of about 5 hours at temperatures of 320 to 425 C.

Example I.`Meml stock loud of about 13,000 pounds 20 opened. Heating element removed. Valve 15 opened, water pressure 42 p. s. l.

Overhead sprinkler 2T turned on. Water spray pressure increased to 55 p. 3.1.

Overhead sprinkler 27 oft. Valve l5 closed. Water pit drained; valve-18 closed, bellraised.

Heating element removed; gas and exhaust on.

Valve 15 opened at 70 p. s. i.

Overhead sprinkler on.

1 hour 150 355 1% hours... 115 305 2 hours. 95 265 2% hours 75 220 3 hours. 60 190 hours...` 25 100 Overhead sprinkler oli; valve 15 closed; water pit drained; Valve 18 closed; bell raised.

Example IIL-Metal stock load of about 14,000 pounds Bell Metal temp. stock Time by Inst. temp. Remarks 26, C. byInst.

0 430 425 Heating element removed; gas and exhaust on. Overhead sprinkler .on lightly. 380 420 Valve l5 opened partially. 350 410 Valve l5 opened at 70 p. s. i. 280 390 Overhead sprinkler on full. 240 370 300 l30 240l 05 190 70 150 50 120 3% hours.. 35 r85 Valve r15 closed, overhead sprinkler oil. 30 80 Bell kept over metal .stock for 20 minutes.

Example I V.-M etal stock load of 22,000 pounds Bell Metal temp. stock 'Time vby Inst. temp. Remarks ,26, C. by Inst.

0 400 320 Heating element removed; gas and exhaust on. 5 mln 340 310 Overhead sprinkler on lightly. l0 min 265 310 Valve 15 opened partially. 15 -min 235 305 Valvel opened at 70 p. s. i. 30 `min 160 290 Overheadsprinkler on full. 1 hour 115 260 1% hours 100 235 2 hours.. 80 200 2% hours. 65 175 3 hours. 55 155 3% hours.-. 50 140 4 hours. 35 120 6 hours 20 85 Overhead sprinkler ot; valve 15 closed, Water pit drained.

5% hours..- Valve 18 closed, bell raised.

With only the overhead sprinkler 27 turned on, the cluration of the cooling ycycle in each of the foregoing examples would have been about 17 hours. By the practice of the invention, this cooling time is decreased to 4 to 5 hours. As a result, the annealed metal can be put back in the production line more rapidly -than heretofore possible. Furthermore, the invention permits the use of an vadditional heating element with the tive bell stations presently required for a single heating element, thus increasing production. And finally, the invention provides yan incentive to decrease the time of the heating or annealing cycle.

I claim:

1. In -the heat-treatment of met-al stock in a bell furnace having a motor-driven fan for providing forced convection currents `within the bell and around the stock as it is heated and subsequently cooled, the improvement yin cooling the heat-treated stock which comprises directing a spray .of Iwater against the rotating blades of the fan, continuously introducing within the `bell a stream of inert gas while simultaneously exhausting from within the bell said gas together with water vapor formed by vaporization of the water spray, and discontinuing said water spray when the temperature of the metal stock has been lowered to within the range of about 110 C. and about 125 C. while continuing said introduction and exhaustion of said gas until substantially 4all water Vapor within the bell has been exhausted.

2. The improvement of claim 1 in which the bell is additionally externally cooled by a water spray directed against the bell near its top. i

3. The improvement of claim 2 in which the atmosphere temperature within the bell is lowered at least 200 C. in about one-half hour by the cumulative eiiect of said inside and outside water sprays.

4. In the heat-treatment of metal stock in a bell furnace having a motor-driven fan for providing forced convection currents within the bell and around the stock as it is heated and subsequently cooled, the improvement in cooling the heat-treated stock which comprises directing a spray of water against the rotating fan until the residual heat of the metal stock is only slightly greater than required to vaporize the spray of water and simultaneously introducing within the bell a stream of inert gas and exhausting from within the bell said gas along with water vapor formed by vaporization of said water spray, continuing said introduction and exhaustion of said gas until substantially all water vapor within the bell has been exhausted, and removing the bell to expose the cooled stock for unloading.

5. In a bell furnace in which metal objects are heated and subsequently cooled with the cooling being obtained at least in part by heat absorbed during the evaporation of atomized Water, a platform for supporting the metal objects, a water atomizing device comprising a motordriven fan beneath said platform, a nozzle placed so as to direct a spray of liquid water against the blades of said fan, a source of liquid water under pressure, said nozzle being connected to said source, whereby liquid water may be directed against the blades of said fan for atomization thereby and subsequent vaporation in said furnace, means for introducing a gas into the bell, means through which gas within the bell may be withdrawn, and a coltrol valve for each of said means.

References Cited in the le of this patent UNITED STATES PATENTS 2,137,868 Wilson Nov. 22, 1938 2,477,796 Germany Aug. 2, 1949 2,557,379 Hancock June 19, 1951 

1. IN THE HEAT-TREATMENT OF METAL STOCK IN A BELL FURNACE HAVING A MOTOR-DRIVEN FAN FOR PROVIDING FORCED CONVECTION CURRENTS WITHIN THE BELL AND AROUND THE STOCK AS IT IS HEATED AND SUBSEQUENTLY COOLED, THE IMPROVEMENT IN COOLING THE HEAT-TREATED STOCK WHICH COMPRISES DIRECTING A SPRAY OF WATER AGAINST THE ROTATING BLADES OF THE FAN, CONTINUOUSLY INTRODUCING WITHIN THE BELL A STREAM OF INERT GAS WHILE SIMULTANEOUSLY EXHAUSTING FROM WITHIN THE BELL SAID GAS TOGETHER WITH WATER VAPOR FORMED BY VAPORIZATION OF THE WATER SPRAY, AND DISCONTINUING SAID WATER SPRAY WHEN THE TEMPRATURE OF THE METAL STOCK HAS BEEN LOWERED TO WITHIN THE RANGE OF ABOUT 110*C. AND ABOUT 125*C. WHILE CONTINUING SAID INTRODUCTION AND EXHAUSTION OF SAID GAS UNTIL SUBSTANTIALLY ALL WATER VAPOR WITHIN THE BELL HAS BEEN EXHAUSTED. 